This invention relates to a power distribution arrangement and more particularly to a power distribution board including a housing cover, an insulating mounting base, and means for securing circuit interrupters to the distribution board.
FIG. 1 is an electrical connection diagram of a power distribution arrangement including main circuit interrupters and shunt circuit interrupters. In FIG. 1, 1 are main circuit interrupters, 2 are source side conductors connected to one side of the main circuit interrupters 1, 3 are connecting conductors connected to the other side of the main circuit interrupters 1, 4 are bus bars connected to the connecting conductors 3 by a suitable means (not shown, 5 are shunt conductors connected to the bus bars 4, 6 are shunt circuit interrupters, and L are loads. The connecting conductors 3 are usually made of rigid material, and the source side conductors 2 are usually flexible.
FIGS. 2 and 3 illustrate a conventional distribution board in which the arrangement shown in FIG. 1 is housed. It is noted that in the prior art power distribution housing, a window formed in a housing cover for providing access to the shunt circuit interrupters is made large for the purpose of accommodating the maximum number of shunt circuit interrupters that is expected to be employed. Therefore, some portions of the window which are not utilized by the shunt circuit interrupters are often exposed. This subjects the customers to great dangers and, therefore, for safety reasons, these open portions of the window must be closed when the shunt circuit interrupters are not in place.
To solve this problem, according to the conventional design shown in FIGS. 2 and 3, a window 10 formed in a housing cover 11 is provided with concealed covers 12 which are integrally formed so that they can be individually punched through each time an interrupter is installed. The concealed covers 12 are so dimensioned that they correspond to the size of a single shunt circuit interrupter 6. While there are two concealed covers 12 in the illustrated design, the number of concealed covers 12 may vary in accordance with the user's needs and utilization.
Since it is necessary with the above-described arrangement to prepare various kinds of housing covers 11 having different numbers of concealed covers 12 and to form the concealed cover 12 integrally with the window 10, a time consuming and troublesome operation for punching through the concealed covers 12 is required.
Another problem in the prior art distribution arrangement surfaces in view of the structure of a conventional shunt circuit interrupter 6, which is shown in FIGS. 4 and 5. An insulating mounting base 15 has support beds 16 disposed at predetermined intervals, and terminals 17 of the shunt conductors 5 extending between the support beds 16. On the other hand, each shunt circuit interrupter 6 includes terminals 19 adapted to be connected to the terminal 17 of the shunt conductor 5. The shunt circuit interrupters 6 are mounted on the support beds 16 in an intimate side-by-side relationship, and their terminals 19 are connected to the terminals 17 of the shunt conductors 5. Exhaust ports 20 are provided on the underside of the shunt circuit interrupters 6.
As previously intended, the shunt circuit interrupter 6 operates when an electric current flowing therethrough exceeds a predetermined value so as to break power supply from the source to the load L. During the interruption, an electric arc is generated and the surrounding gas is ionized. The ionized gas is exhausted from the exhaust ports 20 and some portion of the gas enters into the gap between the bottom of the shunt circuit interrupter 6 and the support bed 16.
Since the shunt circuit interrupters are assembled side by side to form an assembly as shown in FIG. 5, the dielectric strength of the surrounding gas is decreased by the ionized gas and therefore an insulation breakdown often occurs around the exhaust ports or through the bottom portion between the adjacent shunt circuit interrupter.
FIG. 6 is a perspective view of a mounting board for supporting various circuit interrupter assemblies of a power distribution arrangement as shown, 21 is a base plate, 1 is a main circuit interrupter, 3 are connecting conductors connected to the output side terminals of the main circuit interrupter 1, 4 are bus bars connected to the connecting conductors 3 and secured to the base plate 21. In the illustrated example, the bus bars 4 are secured to the base plate 21 in a spaced relationship and individually connected at one end to the connecting conductors 3 by screws 22 and at the other end to an end supporting block 23 by screws 24. Shunt conductors 5 are secured at one end to the bus bars 4 by screws 25 and having terminals 17 at the other end for connecting to shunt circuit interrupters b (not shown in FIG. 6). Insulating mounting bases 15 are provided supporting the shunt circuit interrupters 6 (not shown) and they each have a groove 26 for receiving therein the shunt conductor 5. Tabs 27 are integrally formed to project from the insulating mounting base 15, and are screwed down to the base plate 21 by screws 28, thereby securing the insulating mounting base 15 to the base plate 21.
Since the insulating mounting base 15 of the conventional design is secured in the manner as above described and the tabs 27 must be made to project from the insulating mounting base 15, not only are the tabs 27 often damaged, but also the tabs 27 must be screwed to the base plate 21, resulting in poor assembling efficiency.
Referring now to FIG. 7, mounting structure of the main circuit interrupter 1 will be described. In the figure, 21 is a base plate on which the main circuit interrupter 1 is to be mounted and 30,31 are mounting bases disposed between the bottom of the main circuit interrupter 1 and the base plate 21 and secured to the base plate 21 by a suitable means such as screws 32. The mounting bases 30 and 31 extend in the direction of the width of the main circuit interrupter 1 or in the direction in which the interrupters main 1 are arranged in a side-by-side relationship.
Mounting pawls 33 and 34 project from the mounting bases 30 and 31. The main circuit interrupter 1 is secured to the mounting bases 30 and 31 by inserting the mounting pawls 33, 34 into for engagement with recessed portions 35 and 36 formed at both longitudinal end faces of the main circuit interrupter 1.
Since the conventional main circuit interrupter 1 is mounted on the distribution board as above described, the mounting pawls 33 and 34 must be provided on the respective mounting bases 30 and 31 in order to mount the main circuit interrupter 1 to the mounting bases 30 and 31, and the recessed portions 35,36 must be formed in the end faces of the main circuit interrupter 1 for receiving the engaging mounting pawls 33 and 34. Therefore, the structure is not only complex and expensive, but the efficiency in assembly is low because the mounting pawls 33 and 34 must be brought in engagement with both ends of the main circuit interrupter 1.